This invention relates generally to radiation imagers and in particular to solid state imaging array that are hermetically-sealed from the ambient environment.
Solid state radiation imaging systems are widely used for medical and industrial purposes. Commonly in such systems the radiation desired to be detected is absorbed in a scintillator material and the light photons generated by that absorption are then detected by an imaging array, such as a photodiode array. Both the scintillator material and the silicon-based semiconductive devices (such as photodiodes and thin film transistors (TFTs) used for addressing the photodiodes) in the imaging array are subject to degradation due to exposure to moisture, such as humidity in the ambient air. For example, cesium iodide, a common scintillator material, is hygroscopic, that is, it absorbs moisture from the atmosphere, which results in degradation of its luminescent properties; photodiodes and TFTs exposed to moisture suffer increased electrical leakage in various states of operation, which in turn results in higher noise in the array.
Imaging arrays are typically disposed on a glass substrate and have conductive lines extending to the edge of the substrate to allow connection to external electronic circuits. Currently the imaging array is packaged by placing a moisture barrier cover, such as an aluminum plate, over the array, and coupling the aluminum plate to the glass substrate with an epoxy seal that runs along the perimeter of the plate. Although the epoxy material provides good structural strength, it is an insufficient barrier to the passage of moisture into the imaging array package, especially in environments having high ambient humidity.
It is thus an object of this invention to provide a radiation imager that is effectively hermetically sealed from the ambient environment.